The widespread recognition of the use of radiation to kill or neutralize unwanted cell growth such as cancer has led to increasing interest in various species of radionuclides. Of particular interest are radionuclides which emit alpha radiation, or alpha emitters, because the alpha radiation emitted by these radionuclides does not penetrate deeply into tissue. Thus, by placing alpha emitters adjacent to unwanted cell growth, such as a tumor, the tumor may be exposed to the alpha radiation without undue exposure of surrounding healthy tissue. In many such schemes, the alpha emitter is placed adjacent to the tumor site by binding the alpha emitter to a chelator which is in turn bound to a monoclonal antibody which will seek out the tumor site within the body. Unfortunately, in many instances, the chelator will also bind to metals other than the desired alpha emitter. Since a tumor may have a limited number of sites available for binding with the monoclonal antibody, it is desirable that the number of monoclonal antibodies bonded to metals other than the desired alpha emitter be minimized.
The radioactive decay chains are well known: .sup.233 U (1.62.times.10.sup.5 yr t.sub.1/2) .sup.229 Th (7,340 yr t.sub.1/2).fwdarw..sup.225 Ra (14.8 day t.sub.1/2).fwdarw..sup.225 Ac (10 day t.sub.1/2).fwdarw..sup.213 Bi 47 min t.sub.1/2); and .sup.235 U (7.13.times.10.sup.8 yr t.sub.1/2) .fwdarw..sup.231 Th (25.6 hr t.sub.1/2).fwdarw..sup.231 Pa (3.43.times.10.sup.4 yr t.sub.1/2).fwdarw..sup.227 Ac (22 yr t.sub.1/2).fwdarw..sup.227 Th (18.6 day t.sub.1/2).fwdarw..sup.223 Ra (11.1 day t.sub.1/2). Three alpha emitters particularly well suited for use in medical applications due to their short half lives are Radium-223 (.sup.223 Ra); and Actinium-225 and Bismuth-213 (.sup.225 Ra.fwdarw..sup.225 Ac.fwdarw..sup.213 Bi). Typically, .sup.223 Ra is derived as a daughter product of Thorium-227 which is in turn a daughter product of Actinium-227, (.sup.227 Ac) (Ac "cow"). .sup.227 Ac is normally produced by reactor irradiation of .sup.226 Ra. It is not currently being produced in the U.S. and most of that in existence as well as most of the available .sup.226 Ra exists as wastes or residues from other processes or studies, and, as such, is typically found in a mixture with a wide variety of degraded organic materials and other cations, including Pu, Fe, Co, Cu, and U. As used herein, the terms cation, ion, and metal ion are used interchangeably.
Similarly, .sup.225 Ra/Ac and .sup.213 Bi are daughter products of Thorium-229 (.sup.229 Th) (Th "cow") which is in turn a daughter product of Uranium-233 (.sup.233 U).
Because of the relatively long half-life of .sup.229 Th and the limited decay time of existing stocks of .sup.233 U metal, U.sub.3 O.sub.8, and UO.sub.2, other ions including Pu, Fe, Co, Cu, Pb, etc. generally greatly exceed the .sup.229 Th content on a molar basis. Previously recovered .sup.229 Th contains these and various other impurities including degraded organic materials.
To purify any of these radionuclides from a mixture containing one or more impurities to render the radionuclide in a form suitable for use in medical applications requires that the radionuclides be separated from the impurities. Impurities include but are not limited to any degraded organic compounds and/or cations for example Pu, Fe, Co, Cu, and U. Thus, there exists a need for a method to separate radionuclides from a mixture containing a variety of impurities, especially plutonium for utility in medical therapy.